SEOUL, June 20 (Reuters) - Seoul-based virtual currency exchange Bithumb has been hacked and 35 billion won ($31.51 million) worth of virtual currency held at the exchange stolen, the exchange said on Wednesday.

Bithumb said in a notice on its website that it has stopped all trading after ascertaining “some cryptocurrencies worth about 35 billion won have been seized between late yesterday and early morning today.”

The exchange said it will “make up for the lost cryptocurrencies” with the exchange’s own coins, and has moved all users’ assets into safe “cold wallets”.

A Bithumb official could not be immediately reached by Reuters for further comment.